This invention relates to a facility for assigning transmission channels to terminals of a service-on-demand system.
A service-on-demand system is known, for example, from the journal xe2x80x9cElektronikxe2x80x9d 5/1995, pages 50 to 58. The service-on-demand system contains a server which is connected by an ATM network to a number of hubs which, in turn, are connected to a plurality of BONTs (BONT=Broadband Optical Network Termination). 64 terminals are connected to each BONT via a common coaxial cable. To request a service, a terminal sends a connection request to the server by means of its set-top box. The server makes available to the terminal a transmission channel over which the requested service is transmitted optically to the BONT and then electrically to the terminal. A given number of transmission channels are commonly reserved for each BONT; for example, channels 1 to 32 are assigned to the first BONT, channels 33 to 64 to the second BONT, etc. This is a rigid scheme which only makes available to each terminal the same additional transmission capacity. As a result, for example, only a maximum of 32 of the 64 terminals of each group connected to the BONT can retrieve services simultaneously. If the system is expanded, e.g., by connecting further set-top boxes to an existing BONT, the entire system needs to be shut down to reconfigure the assignment of the transmission channels to the terminals and groups.
It is therefore an object of the invention to organize the assignment of transmission channels to terminals of a service-on-demand system in such a manner that the above disadvantages are avoided.
According to the invention, this object is attained by a facility for assigning transmission channels to terminals of a service-on-demand system, wherein at least two interfaces are provided for connecting the facility to a plurality of terminals, each of the interfaces being connected to a group of terminals by a separate line, that a memory is provided which holds an assignment table containing entries on currently available and currently busy transmission channels for transmitting services requested from terminals, with a variable assignment of transmission channels to terminals being possible regardless of which group the terminals belong to, that a control unit is provided which is connected to the interfaces and the memory, and that the control unit is adapted to receive connection requests from individual terminals for requesting services, to assign at least one transmission channel to each of the individual terminals in response thereto and store the assignment in the memory if in the memory the at least one transmission channel is considered currently available, and to notify the individual terminals that the establishment of a connection is not possible for the time being if in the memory all transmission channels are considered busy. The facility is characterized in that it provides for a variable assignment of transmission channels to terminals, regardless of which group the terminals belong to. For 64+64=128 terminals connected to two BONTs in two groups, for example, 64 transmission channels are provided. The transmission channels are not permanently assigned to the two groups, but are largely freely available to all terminals. For instance, channel 1 may be occupied by terminal 1 of group 1, and channel 2 by terminal 25 of group 2. To be able to reserve a minimum number of freely available transmission channels for each group, 16 of the 64 channels, for example, are reserved as a minimum number for group 1 and another 16 of the 64 channels are reserved as a minimum number for group 2. The remaining 32 channels are then available for use both by terminals of group 1 and by terminals of group 2, depending on traffic volume and demand. This provides flexibility and adapts the assignment of transmission channels automatically to the traffic volume. An added advantage is that more than one transmission channel can be assigned to each terminal, whereby the range of application is increased; for example, services with different transmission capacities for, e.g., different image qualities can be offered for different fees.
According to one advantageous aspect of the invention, the minimum number of reserved transmission channels can be dynamically varied. This offers the additional advantage of an even more flexible assignment of transmission channels. For example, after start-up of a new or expanded system, the minimum numbers can be changed and adapted to the current traffic volume without interrupting service, whereby optimum utilization of the available transmission capacity can be achieved.
According to another advantageous aspect of the invention, the transmission channels can be temporarily blocked in the memory in a virtual fashion. This has the advantage that even during a repair needed in the event of a failure of one or more transmission channels, the system remains limitedly operational as only the channels to be repaired are blocked in a virtual fashion and are thus considered busy.